It is well known to those skilled in the art that polyoxyalkylene-organopolysiloxane copolymers are produced through addition reaction of polyoxyalkylene allyl ethers with organohydrogenpolysiloxanes in the presence of platinum based catalysts, which reaction is commonly referred to as hydrosilylation.
The hydrosilylation reaction is generally carried out in suitable solvents for allowing the addition reaction to proceed smoothly, for example, alcohols such as ethanol and propanol and aromatic hydrocarbons such as toluene and xylene.
JP-A 11-504379 uses as the reaction medium a hydroxyl-free ester solvent which is a liquid with a high boiling point. The use of such a low volatile solvent is advantageous because it helps the hydrosilylation reaction proceed and causes no substantial change in properties of the resulting polyoxyalkylene-organopolysiloxane copolymers even when the solvent is left behind, avoiding any danger like toxicity.
JP-A 2000-234025 describes that the relevant reaction is effected in the presence or absence of a solvent while an amine is added. The amine added can prohibit side reactions particularly when the polyoxyalkylene allyl ethers are terminated with hydroxyl groups.
U.S. Pat. No. 5,869,727 (JP-A 11-116670) discloses that the relevant reaction is effected in vacuum. The vacuum condition ensures formation of a high molecular weight copolymer of [AB]n type using a platinum catalyst, hexachloroplatinic acid and can suppress foaming upon solvent stripping.
For decomposing oxidative impurities which are present in the polyoxyalkylene allyl ether and interfere with hydrosilylation, it is effective to add ascorbic acid, citric acid or derivatives thereof as disclosed in Japanese Patent No. 3299154. This method improves the reactivity of hydrosilylation, but suffers from a problem. When ascorbic or citric acid is used in an amount enough to decompose oxidative impurities (at least 0.01 wt % based on the polyoxyalkylene allyl ether), there is also formed a product of ascorbic or citric acid directly reacting with ≡SiH groups on the organohydrogenpolysiloxane, which can give more or less detrimental effect on the performance of the resulting polyoxyalkylene-organopolysiloxane copolymer.
U.S. Pat. No. 4,847,398, U.S. Pat. No. 5,191,193, and U.S. Pat. No. 5,159,096 describe the addition of additives such as carboxylic acid salts for enhancing reaction activity or suppressing side reactions.
However, all the foregoing methods entail cumbersome steps. Since a noticeable amount of a third substance such as solvent or additive is added, it must be removed from the product after hydrosilylation reaction by such means as stripping or filtering.